The present invention relates to an optical detection device for use in examining a surface of material for a flaw. More specifically, the invention contemplates large-scale, high-speed examination of surfaces which are at least in part reflective for flaws; the reporting of such flaws and the rejection of flawed materials.
The high-speed nondestructive analysis of produced bulk material for quality assurance reasons has been a concern for industry for many years. Without proper control and quality checking, a product can end up at the final consumption location be found lacking in quality, and require return and/or replacement.
Such a late-discovered defect is quite expensive from a manufacturer's standpoint, involving shipping costs, administrative costs, and perhaps most important to a company that strives to achieve a reputation for consistent quality, a loss of customer goodwill.
Many different methods for such nondestructive analysis have been proposed. For example, Peyret et al U.S. Pat. No. 5,164,971 discloses the use of radiographic and tomographic data obtained by an x-ray or gamma-ray source-detector apparatus. An angular rotation of the object results in accommodation of data which is analyzed to reconstruct sections of the object.
Messinger, U.S. Pat. No. 5,265,475 provides for a fiber-optic strain sensor for determining the integrity of critical bonded joints in aerospace applications (including laminates) by embedding a strain sensitive fiber optic cable within the joint or laminate.
Del Grade et al U.S. Pat. No. 5,444,241 discloses a method of detecting flaws in structures by the application of heat to those structures, then scanning the structure for two different wavelengths, obtaining the data as images, and analyzing the images for flaws.
Newman, U.S. Pat. No. 5,146,289 discloses the detection of defects in, e.g. laminates, by the air-coupled acoustic excitation of objects, and use of an interferometer to detect images of the object formed by light reflected from the object. The images are compared and differences provide information on the condition of the object.
Kim et al U.S. Pat. No. 5,094,108 discloses a contact ultrasonic transducer which focuses ultrasonic waves on a point to detect flaws on a surface or subsurface of a substrate. U.S. Pat. No. 5,046,363 also describes the use of acoustic waves to check for voids in a dis-attach layer of integrated circuit packaging. U.S. Pat. No. 5,001,932 discloses a nozzle assembly for discharging water onto a structure so as to prepare it for ultrasonic testing.
Each of these methods or apparatus provides a complex solution to checking manufactured or laminate products for flaws by analysis of collected data, either by complex imaging techniques or algorithmic manipulation of data. Such techniques are not well-adapted to high-speed analysis of great quantities of material.
It, therefore, is an object of the present invention to provide a method of analyzing large quantities of material for defects.
It is a further object of the present invention to provide an apparatus which is capable of analyzing large quantities of material for defects at high speed.
It is yet another object of the present invention to provide a simple optical device which performs the above objects utilizing light scattering or pass through qualities of the surfaces to be analyzed.
The present invention provides a method and apparatus for scanning large surface areas at high speed. A sheet material, preferably a material with a large surface area, is passed along a planar region at a preselected speed. The material is illuminated by a light source such as a fiber optic light source. A detector, such as a ccd linear array, is strategically located such that no light is received by the detector when the surface is flaw-free. For material without flaws, light which is reflected is uniformly reflected, resulting in substantially no scatter of light that might be detected by the detector. In the presence of a flaw, there is sufficient light scatter to be detected by the detector.
In accordance with one aspect of the present invention, an apparatus for the detection of surface flaws in material having a surface which is partially reflective is provided. The apparatus includes at least one light source arranged to direct incident light on a surface of an at least partially reflective material, and a light detector disposed above the surface of the material. The light detector and the at least one light source are arranged relative to each other such that, in the absence of a surface flaw in the material, substantially no light from the at least one light source is detected by the light detector and, in the presence of a surface flaw in the material, light from the at least one light source is reflected off of the flaw and into the detector.
In accordance with another aspect of the present invention, an apparatus for the detection of surface flaws in a reflective material is provided. The apparatus includes a plurality of fiber optic light sources arranged relative to a reflective material to illuminate the surface of the material, a line-scan camera facing a surface of the material, and light baffles separating the light sources and the camera. When the material is moved relative to the camera and no flaw in the material is present, light from the light sources is reflected off of the material and is blocked by the baffles such that no light from the light sources is detected by the detector. When a flaw in the material is present, light from the light sources is reflected off of the flaw such that the baffles to not block the reflected light and the reflected light is detected by the detector.
In accordance with yet another aspect of the present invention, a method for the detection of flaws in material is provided. According to the method, a material having a reflective surface is moved in a direction parallel to the reflective surface. At least one light source and a light detector are arranged relative to each other, and light is emitted from the at least one light source and onto the reflective surface as the reflective surface is moved such that, when no flaw is present in the reflective surface, no light is detected by the light detector. Light reflected from one or more flaws on the reflective surface is detected with the detector.